The long-term goal of this research program is to define the neurochemical mechanisms that mediate the regulation of food intake by the parabrachial nucleus (PBN) in the pons. This application focuses on the role of mu-opioid receptors (muOR) in the PBN in neuronal processes that increase feeding. In preliminary data, infusing the muOR agonist DAMGO into the lateral PBN (LPBN) increased food intake in a behaviorally specific manner. Conversely, acute blockade of muORs reduced feeding. Neuropeptide FF (NPFF) both opposed and mimicked the actions of DAMGO. Immunocytochemical data and analysis of DAMGO stimulated G-protein coupling by [35S]GTPgammaS autoradiography suggested a role for the external lateral subnucleus of the LPBN in these behavioral actions. The proposed studies will use behavioral, pharmacological, immunotoxic, immunocytochemical, autoradiographic, and cellular techniques to: 1) define more precisely the anatomical site and opioid receptor mechanisms for the orexigenic action of DAMGO; 2) assess whether acute and chronic irreversible antagonism of parabrachial uORs reduce food intake; 3) determine whether preferred foods enhances the actions of uOR agonists and antagonists; 4) test the hypothesis that immunotoxic lesions of cells in the LPBN that express uORs will produce hyperphagia; 5) analyze the effects of food restriction and palatable food on opioid receptor mediated G-protein coupling, cfos activation and CREB phosphorylation and on constitutive levels of CREB in the PBN; 6) analyze the interactions of serotonergic, NPFFergic and GABAergic mechanisms with muORs in order to being elucidating the neurochemical organization of parabrachial circuits that regulate feeding; and 7) use sham feeding and flavor preference/aversion conditioning to characterize the behavioral adjustments produced by manipulating muORs, and to test the hypothesis that infusions of DAMGO into the PBN are positively reinforcing. In concert, these studies should provide new data for defining the mechanisms by which opioid neuropeptides in the PBN serve the regulation of food intake. The results should help to define the neurochemical interactions within the circuitry of this brainstem region that direct feeding, specifically, and appetitive reward more generally. Thus, the data may be useful for elaborating novel approaches for treating obesity, eating disorders and behaviors underlying self-administration of substances such as drugs of abuse.